WASHINGTON—President Barack Obama says North Korea will only achieve the security and prosperity it seeks by meeting its international obligations, not by conducting nuclear tests.

Obama called Tuesday's nuclear test by Pyongyang (pyuhng-yahng) a "provocation" and said it will only serve to further isolate North Korea from the rest of the world.

Addressing the issue in his State of the Union speech, Obama said the U.S. will stand by its allies in the region, strengthen its own missile defenses and lead the world in taking "firm action" in response to such threats.

North Korea's official news agency said the test was carried out to counter what it called "ferocious" U.S. hostility that undermines its peaceful, sovereign right to launch satellites.